Use of a mixture of esters of fatty acids as fuel or solvent

ABSTRACT

The invention relates to the use of a mixture, comprising one or more alkyl esters of fatty acids and one or more esters of fatty acids of glycerol carbonate, as a fuel or solvent.

The present invention relates to the use of a mixture, comprising one ormore alkyl esters of fatty acids and one or more esters of fatty acidsof glycerol carbonate, as a fuel or solvent.

More specifically, the present invention relates to the use of the abovemixture as a fuel for diesel engines or as a conventional, industrialsolvent.

The use as fuel for diesel engines of mixtures of alkyl esters, inparticular methyl esters, of fatty acids, deriving from raw materials ofa natural origin, mainly vegetable, such as soybean and rapeseed oils,is well known in the state of the art (so-called bio-diesel:Bio-resource technology, 70, 1-15, 1999). The use of bio-diesel has beenwidely accepted as a result of the considerable advantages it offers,both from an environmental (use of renewable raw materials, generalreduction of exhaust emissions, absence of sulfur) and also motoristicpoint of view (increased lubricity).

Bio-diesel is obtained together with glycerol through thetransesterification of oils or natural fats, consisting of triglyceridesof fatty acids, with an alcohol, usually methanol or ethanol:

wherein:

-   -   R represents a linear, mono- or polyunsaturated alkyl or alkenyl        radical, containing from 8 to 22 carbon atoms;    -   R′ represents a linear or branched alkyl radical containing from        1 to 8 carbon atoms, preferably a methyl or ethyl radical.

The high co-production of glycerol, however, linked to the production ofbio-diesel (over 100 g/kg of bio-diesel) represents a considerabletechnical and economic burden.

On the one hand, glycerol is not adequately placed or fully exploited onthe market, which is even more so with the increase in the productionand use of bio-diesel; on the other hand, the presence of residualglycerol, as such and as mono-, di- and triglycerides, in bio-diesel isnot tolerated, due to problems of de-mixing and fouling.

For the above reasons, it has been necessary to establish narrowspecification ranges: in practice, the free glycerol content inbio-diesel must be lower than 0.02% by weight, and the total glycerol,i.e. both in free form and partially or totally esterified, must belower than 0.25% by weight. Complex separation and purificationoperations are therefore required to meet these specifications.

It has now been found that it is possible to conveniently use, as fuelor solvent, mixtures comprising one or more alkyl esters of fatty acids(bio-diesel) and one or more esters of fatty acids of glycerolcarbonate.

The use of these mixtures as fuel or solvent is particularly interestingas they can be obtained through a process which allows the reuse of theglycerol co-produced together with the production of bio-diesel.

An object of the present invention therefore relates to the use as afuel or solvent, of a mixture comprising one or more alkyl esters offatty acids having formula (I):RCOOR′and one or more esters of fatty acids of glycerol carbonate havingformula (II):

wherein:

-   -   R represents a mono- or polyunsaturated, linear, branched or        cyclic alkyl or alkenyl radical, containing from 4 to 24 carbon        atoms, preferably from 8 to 22 carbon atoms;    -   R′ represents a linear, branched or cyclic alkyl radical        containing from 1 to 8 carbon atoms, preferably a linear or        branched C₁-C₄ radical, more preferably a methyl or ethyl        radical.

The esters of fatty acids of glycerol carbonate are preferably presentin the mixture in a weight percentage ranging from 10 to 40%.

Examples of these esters are represented by the esters of caprylic,lauric, myristic, palmitic, stearic, oleic, linoleic, linolenic acids,or mixtures thereof.

Fats and oils of a natural origin, mainly of vegetable origin, areconveniently used as sources of the above esters, such as, for example,rapeseed oil, soybean oil, palm oil, coconut oil, sunpourer oil, peanutoil, cotton seed oil, sesame oil, or exhausted oils used as food.

The mixtures object of the invention have proved to be suitable for useas fuels in diesel cycle engines, from a combustion and motoristic pointof view, in general. These mixtures typically have net heat values equalto 36-37 MJ/kg and cetane number values higher than 49, values which areentirely similar to those of conventional bio-diesel.

These mixtures have proved to be particularly efficient in the reductionof pollutant emissions, such as carbon monoxide, sulfur dioxide, benzeneand the other incombusted hydrocarbon and particulate, due to their highoxygen content (from 12% to 15% weight), higher than that ofconventional bio-diesel (about 10% weight) and the absence of sulfurcontent.

The mixtures, object of the invention, also have unique solventcharacteristics, which makes them a highly eco-compatible solvent,non-flammable, with a high boiling point and low toxicity, suitable forsubstituting conventional industrial solvents, such as limonene andsolvents of a petroleum origin, currently used in a wide range ofapplications.

Examples of applications are the removal of oils and fats from engines,metal manufactured products, furnaces; degreasing of leather; adhesiveand ink removal; use as releasing agent in the moulding of metal andcement manufactured products; use as solvent and lubricant in metalcutting operations; use as solvent in oil-based paintings.

Alkyl esters of fatty acids (conventional bio-diesel) can be furtheradded to the mixtures, object of the invention, for their use accordingto the purposes of the invention.

When adopted as a solvent, the mixtures can be used as such orformulated with other components such as water and surfactants, whereaswhen used as fuel for diesel cycle engines, they can be used as such oradded to mineral gasoil, for example by adding 5-30 parts in volume ofsaid mixtures to 95-70 parts in volume of gasoil, according to what isknown in the state of the art for the use of bio-diesel.

These formulations can also include conventional quantities of additivesfor enhancing the cetane number, such as peroxides or nitrates,additives for lowering the pour point and for controlling the viscosityand lubricity, stabilizers, detergents, antioxidants, compatibilizingagents.

The mixtures of the invention are obtained in a simple and convenientway, by reaction (transesterification) of one or more esters of fattyacids of glycerol, in particular a triglyceride, or a mixture oftriglycerides of fatty acids, such as those contained in oils and fatsof a natural origin, with one or more alkyl carbonates, in the presenceof a base catalyst, for example by means of the process described ininternational patent application WO 93/09111:

wherein R, the same or different, and R′, again the same or different,have the above-mentioned meanings.

The reaction is carried out in the presence of a catalyst, homogeneousor heterogeneous in the reaction medium, consisting of an organic orinorganic base.

Examples of bases which can be used are alkoxides or carbonates ofalkaline metals, such as, for example, sodium methylate or potassiumtert-butoxide; a guanidine or cyclic guanidine; a hydrotalcite.

The catalyst is generally used in a molar quantity ranging from 1 to10%, with respect to the ester of glycerol used in the reaction.

The oil and fat of a natural origin and the dialkyl carbonate, used asreagents, must have a low water content, above all when the catalystsused are alkoxides or carbonates of alkaline metals. Water, in fact,favours a saponification side-reaction producing soaps which lower theyield of the transesterification reaction.

The water is preferably extracted from the reagents, which is effected,when necessary, before the addition of the catalyst, by means ofazeotropic distillation with an organic azeotrope-forming solvent, forexample a dialkyl carbonate such as dimethyl carbonate (DMC) or diethylcarbonate (DEC), a hydrocarbon such as cyclohexane, hexane, heptane ortoluene, an ether, such as tert-butyl methyl ether or ethyl ether.

When the dialkyl carbonate used in the synthesis of the mixture of theinvention is DMC or DEC, the azeotrope-forming solvent is the dialkylcarbonate itself.

The azeotropic distillation is generally carried out using a quantity ofazeotrope-forming solvent ranging from 2% to 15% by weight of vegetableoil at a temperature ranging from 50° C. to 150° C. and at a pressureranging from 0.2 Ata to 6 Ata.

The oil or fat of a natural origin should have a low content of freefatty acids, preferably not higher than 1 mg KOH/g, to avoid theexcessive consumption of catalyst and excessive formation of soaps whichreduce the transesterification yield.

The reaction is generally carried out at a temperature ranging from 60°C. to 150° C. for times varying from 1 to 24 hours, using a molar ratioof the alkyl carbonate with respect to the ester of glycerol used in thereaction ranging from 1 to 6.

The alkyl carbonate is preferably used in excess as it also acts asreaction solvent. The reaction can be carried out batchwise, insemi-continuous or in continuous in a nitrogen atmosphere or underautogenous pressure, generally ranging from 1 Ata to 6 Ata.

The product is isolated and purified using conventional techniques suchas neutralization and subsequent removal of the catalyst by filtrationor separation of the catalyst in a de-mixed liquid phase; the possibleremoval of the excess of alkyl carbonate by distillation; washing withwater or aqueous acids; extraction with an organic solvent, for examplea hydrocarbon such as hexane, cyclohexane or heptane, an ether such asethyl ether or tertbutyl methyl ether, a dialkyl carbonate.

When the triglycerides used in the reaction are those present in oils ofa vegetable origin, such as soybean oil or rape oil, the mixtures,object of the invention, are liquid at room temperature and can be mixedin all proportions with the hydrocarbons and oil distillates, such asgasolines and gasoil in particular.

The following examples are provided for illustrative purposes and do notlimit the scope of the present invention.

In these examples, the transesterification reaction is carried out in ajacketed glass reactor, having a volume of 5 liters, heated bycirculation in the jacket of oil coming from a thermostat-regulatedbath. Said reactor is equipped with a water-cooled condenser, amechanical stirrer, a thermometer, a plunge-pipe for collecting samplesand a glass distillation column with 15 perforated plates, having aninternal diameter of 2.5 cm. All the vapour is condensed at the head ofthe column and only a part of the liquid is removed, at the reflux ratioestablished by the intervention of an electromagnetic valve.

EXAMPLE 1

The following reagents are added to the reactor described above: 2042 g(2.34 moles) of soybean oil and 782 g of dimethyl carbonate. Thestirring is activated and the reactor is heated with an oil baththermostat-regulated at 115° C. In order to eliminate the water from thereagents, 150 g of dimethyl carbonate are distilled with a reflux ratioequal to 2. The mixture is left to cool to room temperature which nowcontains 632 g of dimethyl carbonate (7.02 moles) and 21.6 g of asolution of sodium methoxide at 30% by weight in methanol (0.12 moles ofsodium methoxide) are added. The reactor is heated again so as to obtainan internal temperature of 90° C. After about 6 hours at a temperatureof 90° C., the conversion of the soybean oil is higher than 99%.

The reactor is left to cool to room temperature and 17.3 g of a solutionof phosphoric acid at 85% by weight in water (0.15 moles of phosphoricacid) are added to neutralize the catalyst. The mixture is left understirring for about 30 minutes and subsequently transferred to anapparatus consisting of a flask and a Claisen condenser where 368 g of adistillate having the following composition is removed, by distillationat a temperature of 80° C. and a reduced pressure of 15 mbar:

-   -   97.3% by weight of dimethyl carbonate, 2% by weight of methanol        and 0.7% by weight of water.

Gaschromatographic analysis reveals the presence of 1% by weight ofdimethyl carbonate (23.5 g) in the raw residual mixture, which is almostentirely removed by further distillation at a temperature of 90° C. anda pressure of 2 mbar for a period of 2 hours. The precipitate containingsodium monobasic phosphate, methylcarbonate of glycerol carbonate,glycerol carbonate and small quantities of methyl esters of fatty acidsand esters of fatty acids of glycerol carbonate is filtered. The liquidraw mixture, having a weight of 2248.7 g, has the following composition,determined by means of HPLC and ¹³C NMR analyses:

-   -   24.8% by weight of esters of fatty acids of glycerol carbonate,        71.4% by weight of methyl esters of fatty acids, 1.2% by weight        of glycerol carbonate, 1.8% by weight of methyl carbonate of        glycerol carbonate, 0.17% by weight of diglycerides, 0.19% by        weight of triglycerides and 0.4% by weight of dimethyl        carbonate.

The methyl carbonate of glycerol carbonate is slowly separated byprecipitation from the mixture obtained, which is liquid at roomtemperature.

This mixture can be used without any further treatment in theformulations of solvents which contain components capable of allowingthe dissolution of the methyl carbonate of glycerol carbonate.

For all the other applications, the mixture was further purified.

EXAMPLE 2

Purification of the Raw Mixture

The raw mixture is diluted in a separating funnel with 1 litre oftert-butyl methyl ether (MTBE) and washed with three 500 ml portions ofdistilled water. The aqueous washings are then extracted with 500 ml ofMTBE. The two organic phases in MTBE are combined and concentrated bydistillation of the MTBE in a rotating evaporator at 80° C. and aminimum pressure of 15 mbar. Gaschromatographic analysis reveals thepresence in the residual mixture of 1.5% by weight of MTBE, which isremoved by further distillation at a temperature of 90° C. and apressure of 2 mbar. The residual mixture, having a weight of 2113.8 ghas the following composition, determined by means of HPLC and ¹³C NMRanalyses:

-   -   25.6% by weight of esters of fatty acids of glycerol carbonate,        73.56% by weight of methyl esters of fatty acids, 0.4% by weight        of methyl carbonate of glycerol carbonate, 0.07% by weight of        glycerol carbonate, 0.17% by weight of diglycerides and 0.20% by        weight of triglycerides.

This mixture is characterized by the following physico-chemicalproperties: density (20° C.) (g/ml) 0.904 viscosity (20° C.) (Cst) 9.7viscosity (40° C.) (Cst) 5.6 pour point (° C.) −2 flash point (° C.)(closed vase) >120 boiling point (° C.) (TGA) >300 sulfate ashes (weight%) 0.0016 interfacial pressure (20° C.) (mN/m) 31.3 acid number (mgKOH/Kg) 0.3 sodium content (mg/Kg) <0.5 phosphorous content (mg/Kg) <3water (mg/Kg) 200 cetane number 50.1 gross heat value (MJ/Kg) 38.77 netheat value (MJ/Kg) 36.305

EXAMPLE 3

The following reagents are added to the reactor described above,excluding the distillation column: 2034.5 g (2.33 moles) of soybean oil,636 g (7.07 moles) of dimethyl carbonate and 16.7 g of1,5,7-triazabicyclo[4.4.0]dec-5-ene (0.12 moles). The stirring isactivated and the reactor is heated with an oil baththermostat-regulated so as to have an internal temperature of 80° C.After about 6 hours at a temperature of 80° C., the conversion ofsoybean oil is higher than 99%.

The reactor is left to cool to room temperature. During the cooling, thereaction mixture is separated into two phases; a lower phase having aweight of 171.4 g and an upper phase having a weight of 2515.8 g. Thelower phase has the following composition determined by means of HPLCand ¹³C NMR analyses:

-   -   9.7% by weight of 1,5,7-triazabicyclo[4.4.0]dec-5-ene, 12.9% by        weight of dimethyl carbonate, 3.3% by weight of methanol, 28.9%        by weight of glycerol carbonate, 26.9% by weight of methyl        carbonate of glycerol carbonate, 1.5% by weight of bis carbonate        of glycerol carbonate, 3.4% by weight of esters of fatty acids        of glycerol carbonate and 13.4% by weight of methyl esters of        fatty acids.

The upper phase is transferred to an apparatus consisting of a flask anda Claisen condenser where 340.8 g of dimethyl carbonate are removed, bydistillation at a temperature of 80° C. and a reduced pressure of 15mbar.

Gaschromatographic analysis reveals the presence of 1% by weight ofdimethyl carbonate (21.8 g) in the raw residual mixture, which is almostentirely removed by further distillation at a temperature of 90° C. anda pressure of 2 mbar for a period of 2 hours. The raw mixture, having aweight of 2161.8 g, has the following composition, determined by meansof HPLC and ¹³C NMR analyses:

-   -   23.6% by weight of esters of fatty acids of glycerol carbonate,        73.8% by weight of methyl esters of fatty acids, 0.5% by weight        of glycerol carbonate, 1.4% by weight of methyl carbonate of        glycerol carbonate, 0.16% by weight of diglycerides, 0.18% by        weight of triglycerides and 0.4% by weight of dimethyl        carbonate.

The methyl carbonate of glycerol carbonate is slowly separated byprecipitation from the mixture obtained, which is liquid at roomtemperature.

This mixture can be used without any further treatment in theformulations of solvents which contain components capable of allowingthe dissolution of the methyl carbonate of glycerol carbonate.

For all the other applications, the raw mixture must be furtherpurified, using the procedure illustrated in Example II.

The mixture coming from the purification treatment, having a weight of2053.7 g, has the following composition, determined by means of HPLC and¹³C NMR analyses:

-   -   24% by weight of esters of fatty acids of glycerol carbonate,        75.2% by weight of methyl esters of fatty acids, 0.4% by weight        of methyl carbonate of glycerol carbonate, 0.08% by weight of        glycerol carbonate, 0.16% by weight of diglycerides, 0.19% by        weight of triglycerides.

This mixture is characterized by the following physico-chemicalproperties: density (20° C.) (g/ml) 0.902 viscosity (20° C.) (Cst) 9.42viscosity (40° C.) (Cst) 5.53 pour point (° C.) −2 flash point (° C.)(closed vase) >120 boiling point (° C.) (TGA) >300 interfacial pressure(20° C.) (mN/m) 30.9 water content (mg/Kg) 220 cetane number 49.0 grossheat value (MJ/Kg) 38.705 net heat value (MJ/Kg) 36.26

1. The use as a fuel or solvent of a mixture comprising one or morealkyl esters of fatty acids having formula (I):RCOOR′ and one or more esters of fatty acids of glycerol carbonatehaving formula (ii):

wherein: R represents a mono- or polyunsaturated, linear, branched orcyclic alkyl or alkenyl radical, containing from 4 to 24 carbon atoms;R′ represents a linear, branched or cyclic alkyl radical containing from1 to 8 carbon atoms.
 2. The use according to claim 1, wherein in theesters having formula (I) and (II): R represents a mono- orpolyunsaturated, linear, branched or cyclic alkyl or alkenyl radical,containing from 8 to 22 carbon atoms; R′ represents a linear or branchedalkyl radical containing from 1 to 4 carbon atoms.
 3. The use accordingto claim 1 or 2, wherein the esters of fatty acids of glycerol carbonateare present in the mixture in a weight percentage ranging from 10 to40%.
 4. The use according to any of the previous claims, as fuel fordiesel cycle engines.
 5. Fuel compositions comprising the mixture ofesters as defined in claims 1 to 3, added to mineral gasoil.
 6. Fuelcompositions comprising the mixture of esters as defined in claims 1 to3, and at least one additive for fuels.
 7. The use according to claims1, 2 or 3 as a conventional industrial solvent.
 8. Solvent compositionscomprising the mixture of esters as defined in claims 1, 2 or 3,formulated together with water and surfactants.
 9. A process for thepreparation of a mixture comprising one or more alkyl esters of fattyacids having formula (I):RCOOR′ and one or more esters of fatty acids of glycerol carbonatehaving formula (II):

wherein: R, the same or different, and R′, also the same or different,have the meanings illustrated above, comprising the reaction in theabsence of water of one or more esters of fatty acids of glycerol, withone or more alkyl carbonates, in the presence of a base catalyst,according to the following reaction scheme:

and the purification of the mixture obtained by means of neutralization,removal of the catalyst, washing with water or aqueous acids and,finally, extraction with an organic solvent.
 10. The process accordingto claim 9, wherein, before the addition of the catalyst, the water isextracted from the reagents by means of azeotropic distillation with anorganic azeotrope-forming solvent.
 11. The process according to claim10, wherein, when the alkyl carbonate to be reacted is dimethylcarbonate or diethyl carbonate, the azeotrope-forming solvent consistsof the same dialkyl carbonates.